Solution for depositing an electroless cobalt alloy

ABSTRACT

ADDITIONS TO AN ELECTROLESS COBALT SOLUTION OF SODIUM TUNGSTATE, POTASSIUM PERRHENATE, NICKEL SULFATE OR PHENYLTHIOUREA YIELDED ELECTROLESS COBALT ALLOY DEPOSITS HAVING A VARIETY OF IMPROVED MAGNETIC PROPERTIES.

y 11', 1971 F. PEARLSTEIN ETAL 3,578,468

7 SOLUTION FOR DEPOSITING AN ELECTROLESS COBALT ALLOY 4 Sheets-Sheet 1 Filed March 1, 1968 ADDITIONS OF N02 L O R T N 0 C U A B o c S S E L 1% T C G L IE FF O3g/l AlOg/l 40 DEPOSIT WEIGHT, mg.

FIG. 2

-- ELECTROLESS COBALT CONTROL ADDITIONS OF KReO WT m TI .0 S MW RAE W N ED uw WFR 4'0 6 0 DEPOSIT WEIGHT, mg.

nw O 5 23 15 t 6mmou IOO- ATTORNEYS F. PEARLSTEIN ETAL 3,578,468

SOLUTION FOR DEPOSITING AN ELECTROLESS COBALT ALLOY May 11, 1971 I 4 Sheets-Sheet 2 FIG. 3

Filed March 1,

NO w O I Cnunw T.

mm M 0 O I C q 8 SF L o 0 O 6 Rm T NW ED w mu m w M210. w 4 3 2 DEPOSIT WEIGHT, mg. EFFECT OF NICKEL SULFATE ADDITIONS TO ELECTROLESS COBALT SOLUTION ON COERCIVITY OF DEPOSITS ELECTROLESS COBALT CONTROL ADDITIONS OF PHENYL THIOUREA FIG. 4

w w 4w.

EFFECT OF PH ENYLTHIOUREA ADDITIONS TO ELECTROLESS COBALT FRED PEARLSTEIN ROBERT E WEI HTMAN 5W4 )4 fl vWM ATTORNEYS SOLUTION ON THE COERCIVITY OF DEPOSITS [NVENTQRS F. PEARLSTEIN ETIAL 3,578,468

May 11, 1971 SOLUTION FOR DEPOSITING AN ELECTROLESS COBALT ALLOY Filed March 1, 1968 4 Sheets-Sheet 5 8'0 DEPOSIT WEIGHT, mg.

N mm 0 WW w w 5 M mm W 0 M H R s EDE IO U WWY W A WFRB A was C S 0 ED.- m O S m EE L G W EW' 0 s um. wR HE DH OT A F O T C E F F E y 11, .1971 F; PEARLSTEIN ErAL 3,578,468

v SOLUTION FOR DEPOSITING AN ELECTROLESS COBALT ALLOY- Filed March 1, 1968 4 She ts-Sheet 4 FIG.6

' {.ELECTROLESS COBALT CON'I'ROL lOg/l NO WQ d2H2O added 0.3 g/l KReO udded 3 g/l NiSO GH O added 0.9 mg/l PHENYLTHIOUREA lOg/l NiSO -6H O added added EFFECT OF METAL SALT ADDITIONS TO ELECTROLESS .COBALT SOLUTION ON THE HYSTE ESIS LOOPS OF DEPOSITS (l|,000 TO I3,000 THICK.)

INVENTOR.

United States Patent 3,578,468 SOLUTION FOR DEPOSITING AN ELECTROLESS COBALT ALLOY Fred Pearlstein and Robert F. Weightman, Philadelphia,

Pa., assignors to the United States of America as represented by the Secretary of the Army Filed Mar. 1, 1968, Ser. No. 709,620

Int. Cl. C23c 3/02 US. Cl. 106-1 6 Claims ABSTRACT OF THE DISCLOSURE Additions to an electroless cobalt solution of sodium tungstate, potassium perrhenate, nickel sulfate or phenylthiourea yielded electroless cobalt alloy deposits having a variety of improved magnetic properties.

The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to the electroless deposition of cobalt alloys from novel bath compositions and more particularly concerns such alloys having improved coercivity, remanence, and squareness properties.

It is well known that cobalt is a highly magnetic material, being considerably more so than nickel. In view thereof and to the continued widespread interest in magnetic films for information storage on tapes, discs, and drums, it would be highly advantageous if electroless cobalt alloys could be produced having improved magnetic properties.

It is therefore an object of this invention to provide electroless cobalt alloys.

Another object of the invention is to provide such alloys having improved magnetic properties, and thus being suitable for use in information storage devices.

Other objects and advantages of the invention will become apparent to those skilled in this art from the appended claims and following description of the invention made in conjunction with the accompanying drawings wherein:

FIGS. 1, 2, 3, and 4 are graphical representations showing the respective effects of sodium tungstate, potassium perrhenate, nickel sulfate, and phenylthiourea additions to an electroless cobalt solution on the coercivity of deposits.

FIG. 5 graphically illustrates the effects of various additions to electroless cobalt solutions on the remanence of deposits; and

FIG. 6 illustrates a series of curves showing effects of certain metal salt additions to electroless cobalt solutions on the hysteresis loops of deposits.

In achieving the objects aforementioned, copper strips (1.1 x 10.2 x 0.08 cm.) were abrasive tumbled to remove burrs and surface imperfections therefrom and then chemically polished by a ten minute immersion in a solution consisting of 15% by volume of nitric acid having a specific gravity of 1.42 and 85% by volume of equal portions of glacial acetic acid and phosphoric acid, the solution being maintained at about 25 C. The strips were then rinsed and activated for electroless deposition by a 30 second immersion in a solution consisting of 0.1 g./l. palladium chloride and 0.1 ml./l. hydrochloric acid, maintained at about 25 C. The strips were then rinsed, dried, and weighed, and immersed into electroless plating solutions at 95 :1 C. Deposit weights were determined by weight gain measurements.

The electroless cobalt solution used as a basis for produclng alloy deposits consisted of:

30 g./l. cobalt chloride.6H O

g./l. sodium citrate.2H O

50 g./l. ammonium chloride 20 g./l. sodium hypophosphite.H O 60 ml./l. ammonium hydroxide The solution had an initial pH of about 8.9 which decreased to about 8.8 after deposition tests the pH being measured at room temperature.

The deposits produced on the copper strips were examined for coercive force and remanent magnetization using a commercial testing device having a drive field of 60 cycles per second and field intensity adjustable from 0 to 2000 oersteds.

As shown in FIG. 1, additions of 1 to 10 g./l. sodium tungstate.2H O to the electroless cobalt solution yielded deposits having moderately increased coercivities over electroless cobalt alone. The remanence of the deposits was not significantly affected.

It will be seen from FIG. 2 that additions of 0.1 g./l. potassium perrhenate to electroless cobalt solutions had little effect on coercivity. Additions of 0.3 g./l. reduced coercivity slightly. When 0.8 g./l. potassium perrhenate 'were added, the usual trend of increased coercivity with decreasing deposit weight was reversed, i.e., thin coatings possessed low coercivities whereas heavier deposits were found to have increased coercivities. The remanence of deposits from solutions containing 0.3 g./l. or more potassium perrhenate were substantially reduced over those containing electroless cobalt alone.

Referring now to FIG. 3, the addition of 1 or 3 g./l. nickel sulfate hexahydrate to electroless cobalt solutions resulted in a considerable increase in the coercivity of the deposit. With deposits made from solutions containing 3 g./l. nickel sulfate hexahydrate, the coercivity tended to remain relatively constant with deposit weight which may be attributable to variations in deposit composition with thickness. Ten g./l. nickel salt addition produced deposits having negligible coercivity but high remanence. In general, the remanence of these deposits increased with nickel sulfate additions to the cobalt bath.

As shown in FIG. 4, additions of phenylthiourea of 0.1 or 0.3 mg./l. to electroless cobalt solutions provided deposits not significantly altered in coercivity, but at 0.9 mg./l. addition, there was substantial lowering of coercivity, probably due to decreased phosphorus content of deposits. Increased concentrations of phenylthiourea resulted in increasing remanence.

The changes in remanence of deposits, as illustrated in FIG. 5, were most pronounced from electroless cobalt solutions to which had been separately added 0.3 g./l. potassium perrhenate, 3 g./l. nickel sulfate.6H O or 0.9 mg./l. phenylthiourea.

Hysteresis loops of many shapes were found for the various cobalt alloy depoits (FIG. 6), each of the deposits being between about 11,000 to 13,000 A. thick. For example, additions of 0.3 g./l. potassium perrhenate to an electroless cobalt solution yielded deposits having a hysteresis loopof considerably decreased remanence and squareness. The squareness of the hysteresis loop of deposits of an electroless cobalt solution to which 3 g./l. nickel sulfate hexahydrate had been added was increased. The effect of 0.9 mg./l. phenylthiourea addition on the loop shape of deposit may be seen in FIG. 9. The shape reflects the relatively low coercivity and high remanence. Rather unusual hysteresis loops were produced with deposits from an electroless cobalt solution containing 10 g./l. nickel sulfate hexahydrate. The loop reflects 10w coercivity, high remanence and high squareness and indicates that reversal of polarity can be achieved with little energy consumption.

In actual practice, sodium tungstate, potassium perrhenate, nickel sulfate and phenylthiourea may be readily dissolved in the electroless cobalt solution by adding as a powder thereto. Phenylthiourea, however, may conveniently be dissolved in acetone which may then be added to the cobalt solution. The acetone will readily evaporate at the operating temperatures imparting no deleterious etfects whatsoever to the final bath composition.

Electroless cobalt deposits tarnish readily when exposed to salt conditions to form a very unpleasant-appearing mottled brown condition. It was found that certain electroless cobalt alloys were considerably more resistant to tarnishing during exposure to five percent neutral spray. Additions to the aforementioned cobalt solution of g./l. sodium tungstate dihydrate, 0.9 mg./l. phenylthio- 30 g./l. cobalt chloride hexahydrate 80 g./l. sodium citrate dihydrate 50 g./l. ammonium chloride g./l. sodium hypophosphite monohydrate 60 ml./ ammonium hydroxide and a compound added thereto selected from the group consisting of sodium tungstate dihydrate, potassium perrhenate, and phenylthiourea.

2. The solution as described in claim 1 wherein said 4 compound comprises between about 0.1 to 10 g./l. of sodium tungstate dihydrate.

3. The solution as described in claim 1 wherein said compound comprises between about 0.3 to 0.8 g./l. potassium perrhenate.

4. The solution as described in claim 1 wherein said compound comprises about 0.9 m g/l. phenylthiourea.

5. A solution for depositing a tarnish resistant electroless cobalt alloy comprising about 30 g./l. cobalt chloride hexahydrate 80 g./l. sodium citrate dihydrate g./l. ammonium chloride 20 g./l. sodium hypophosphite monohydrate ml./l. ammonium hydroxide and a compound added thereto selected from the group consisting of sodium tungstate dihydrate, phenylthiourea, sodium arsenate heptahydrate, and ferric sulfate.

6. The solution as described in claim 5 wherein said sodium tungstate dihydrate is present in an amount of about 10 g./l., said phenylthiourea is present in an amount of about 0.9 mg./l., said sodium arsenate heptahydrate is present in an amount of about 1 g./l., and said ferric sulfate is present in an amount of about 1 'g./l.

References Cited UNITED STATES PATENTS 3,271,140 9/1966 Freche et a1. -170 3,415,643 12/1968 Freche et al 75170 3,450,580 6/1969 Hadfield et al 75-170 RICHARD O. DEAN, Primary Examiner U.S. Cl. X.R. 117l30, 234 

